Specifications

Functional Description
RADring
Installation & Operation Manual
2-34 RI/RO Modules Functional Description 3/11/98 12:33
Cable Break Protection
All the RAD TFR repeater models include cable break protection. A dip
switch located on the TFR card allows the user to disable this function when
one TFR operates in a link terminated at the other end in a fiber-optic
repeater or converter using an incompatible cable break protection method
or no cable break protection at all.
The cable break protection function automatically detects breaks in the
fiber-optic cable and loops the main path to the back-up path, in order to
maintain ring continuity. This is illustrated in the diagram below, which
indicates what happens on the fiber-optic segment when one of the cable
fibers breaks or is accidentally disconnected at an optical patch panel.
CABLE
BREAK
TFR TFR
FIBER-OPTIC
RECEIVER
FIBER-OPTIC
RECEIVER
FIBER-OPTIC
TRANSMITTER
FIBER-OPTIC
TRANSMITTER
MAIN
PATH
MAIN
PATH
BACKUP
PATH
BACKUP
PATH
TX RX
RX TX
SITE A
RO SIDE
REPEATER
REPEATER
FAULT
LIGHTS
FAULT
BLINKS
SITE B
RI SIDE
Figure 2-25 TFR Cable Break Protection
Should the fiber connected to the RX connector of site A break, the TFR
detects the loss of the optical signal and carries out the following actions:
1. Loops the main path to the back-up path after passing through the
repeater section. This ensures that the TFR returns a regenerated ring
signal.
2. Sends a fault pattern on the TX fiber. The TFR at site B detects this
pattern and loops the main path to the backup path (after regeneration
of the signal by the repeater).
These two actions maintain ring continuity in case of a break in the fiber-optic
segment.
To notify the user that a fault condition exists, the two TFRs provide fault
indication as follows:
•
At the receiving TFR, the FLT indicator lights continuously to indicate that
the receive light is missing.
•
At the second TFR, the FLT indicator flashes to indicate that the transmit
fiber is disconnected.
•
The cable break detection operates even when the Token Ring network is
inactive, e.g. when all the stations are deinserted and there is no ring
signal.